1. Field of the Invention
The invention is directed to a process of depositing silicon oxynitride and silicon dioxide in a manner such that these chemically amplified photoresist are not contaminated from amine groups or dangling bonds as a result of using high density plasma(HDP). In general, the invention is accomplished by depositing silicon oxynitride DARC and silicon dioxide using a high density plasma (HDP) CVD system at a lower than usual pressure range and at higher power, thereby permitting the use of O.sub.2 gas as an oxygen source of DARC.
2. Description of the Prior Art
Silicon oxynitride DARC, has been broadly used for DUV lithography, and is especially attractive for improving lithographic process windows because of its tunable refractive index and high etch selectivity to resist. Resist contamination is one of the greater concerns in the use or application of silicon oxynitride films; especially due to the presence of amine radicals, which are known to contaminate chemically amplified resists by neutralizing the acid catalyst, and rendering that portion of the resists insoluble in the developer.
The imaging mechanism of chemically amplified photoresist is a photo-acid generator that receives photons from radiation, that generates an acid to catalyze the chemical reaction. This changes the resist solubility that can be removed with the developer. The catalytic acid generated into photo exposure is essential to chemically amplified resist. Any environmental contamination, or other acid depleting process or substrate contamination effects can cause abnormal resist profiles.
Chemically amplified positive resist tend to present themselves as a "foot" over the nitrogen contained substrates, such as silicon oxynitride, silicon nitride, and titanium nitride. The amount of contamination also strongly depends on resist chemistry.
The typical method of preventing the resist contamination from silicon oxynitride is to deposit an additional silicon dioxide and/or plasma treatment to oxidize the surface of silicon oxynitride. In this method, the RF PECVD (plasma enhanced chemical vapor deposition) is operated in a vacuum system, and the pressure range in this system is from 1 torr to 20 torr. Conventional DARC films are deposited at about 1.5 torr 10 torr pressure range. In this pressure range, O.sub.2 gas cannot be used because of explosion risk. Therefore, N.sub.2 O gas is usually used as an oxygen source of both silicon oxynitride and silicon dioxide. Putting it another way, even though there is an additional silicon dioxide film as a barrier layer, this layer may contain nitrogen and/or an amine group from N.sub.2 O reaction gas. Depending upon the sensitivity of the chemically amplified photo resist to nitrogen content in the substrate film, extremely small amounts of amine group or dangling bonds at the surface can cause photoresist contamination, as shown in FIG. 1.
U.S. Pat. No. 5,614,055 disclose a high density plasma CVD and etching reactor. In particular, the plasma reactors of the embodiments of FIGS. 6 and 8 are used in performing any CVD thin film deposition. In col. 10, lines 16-23 it is indicated that these reactors are especially useful for any deposition of films using highly reactive chemical precursor species such as silane. It is further disclosed at this portion of said patent that the reactor can be used for thin films other than silicon dioxide, such as diamond, and that deposition of material having a high dielectric constant can be carried out as well by these embodiments.
The plasma process of the '055 patent is accomplished by: providing a vacuum processing chamber holding a work piece to be processed and having on one side thereof an antenna comprising a substantially dome-shaped portion at least partially surrounding a plasma generating region and a vertical cylindrical portion which underlies said substantially dome-shaped portion; feeding a processing gas including an electronegative gas into said processing chamber; resonantly coupling an RF electrical signal to said antenna; and non-resonantly and inductively coupling electromagnetic energy from said antenna into a plasma formed in said plasma generating region of said processing chamber from said processing gas, whereby said work piece is processed by said plasma.
In the plasma process of the '055 patent, the electronegative gas may comprise a halogen and the processing gas may additionally comprise a precursor gas for silicon dioxide.
A plasma processing method for forming a film by a plasma CVD process is disclosed in U.S. Pat. No. 5,626,922, in which a high density plasma is generated in the presence of a magnetic field.
At column 2, line 63 to column 3, line 15 of the '922 patent, it is indicated that, to generate and maintain a high density plasma at a pressure as high as the range of from 0.03 to 30 torr, an ECR is generated in a columnar space under a low vacuum. Thereafter, a gas, liquid or solid is introduced into the columnar space to produce a plasma which is maintained under high pressure so as to obtain a space having a highly concentrated product gas larger than the gas concentration normally used in a conventional ECR CVD process.
The disclosure in the immediately preceding paragraph indicates that films obtained include carbon films, diamond films, i-carbon, DLC and insulating ceramics, metallic films, and in particular films of metal having a high melting point.
U.S. Pat. No. 5,721,021 discloses a method of depositing titanium-containing conductive thin film using a high density plasma CVD. In particular, a low-pressure high-density plasma is generated with an output of the radio-frequency power of 2.5 kW to deposit a titanium nitride film at a rate of about 30 nm/min. The resultant titanium nitride film has a chlorine content of 1% or less, metallic luster and low resistance.
Accordingly, one significant disadvantage of prior methods of preparing silicon oxynitride DARC is the presence of resist contamination, and this resist contamination remains intact despite the use of additional silicon dioxide and/or plasma treatment to oxidize the surface of silicon oxynitride.
Another disadvantage of the prior art processes of preparing silicon oxynitride DARC is that, when a RF PECVD is utilized, the process must proceed in a vacuum system at a pressure range of from about 1 torr to about 20 torr, most typically, deposition of the DARC films are deposited at a pressure range of from about 1.5 torr 10 torr; however, in this pressure range, O.sub.2 gas cannot be used due to the risk of explosion.
A further disadvantage of prior methods of preparing silicon oxynitride DARC is that, since O.sub.2 gas cannot be used due to explosion risk, N.sub.2 O gas is used as an oxygen source for both silicon oxynitride and silicon dioxide; however, the use of the N.sub.2 O gas when an additional silicon dioxide film is used as a barrier layer renders the process at risk of containing nitrogen and/or an amine group from the N.sub.2 O reaction gas. Therefore, depending upon the sensitivity of the chemically amplified photoresist to the nitrogen content in the substrate film, extremely small amounts of the amine group or dangling bonds at the surface tend to cause photoresist contamination, as evidenced by a "foot" over a nitrogen containing substrate, such as silicon oxynitride, silicon nitride, and titanium nitride.